With some columnar in-memory data stores, column values can be dictionary compressed. Such compression is such that each distinct value in a column is mapped to a unique integer value. This mapping is one-to-one. These integer values are sometimes referred to a value IDs or vids as shorthand for value identifiers. Associated to each column there is a vector of these vids which can be referred to as a column data array or an index vector. For a column c, a vid v in position p of the index vector for c indicates that for column c, the row at position p has the value associated to v. For storage efficiency, the vids in the vector can be packed so that only n-bits are used to represent each vid in the vector with n the number of bits needed to represent the highest vid. For example, if n is equal to 2, in the first 64 bits of the index vector, the vids for the first 32 rows in the column can be stored.